The use of dc-to-ac PWM inverters in adjustable speed drives for controlling loads is becoming increasingly popular. A motor can be driven in an ac synchronous mode or brushless dc (BLDC) mode using a dc link inverter to control three-phase switching of current in the windings of a 3-phase motor.
One object of the invention is to increase efficiency and to lower the cost of manufacture by integrating electromagnetic components.
When the power supply is a dc source, it is desirable to have other auxiliary dc and ac power components of different voltages operated from the sole dc power source. It may also be desired to convert energy from a low voltage dc supply back to the high power dc power source. There are many dc-to-dc converters that can be used to supplement a main ac inverter, but these are separate components. The present invention is designed for application in an apparatus which combines one or more dc-to-dc or dc-to-ac conversions with a motor being controlled by the main inverter.
The increasingly sophisticated application of the contemporary technology often calls for several electromagnetic devices to be used simultaneously. For example, in certain uses of electric motors it is desirable to add various associated devices such as the auxiliary power systems, filters, transformers, and chokes. This creates an opportunity for cost reduction by forming multiple devices from individual components.
The present invention provides a method and an electronic motor control that utilize zero-sequence components to provide dc-to-dc power conversion for low voltage dc devices operated in a circuit with a larger component, such as a motor. Such low voltage dc devices can include, but are not limited to, dc-to-dc converters, transformers, filter chokes, ac output power supplies, and smoothing filters for the main stator windings in PWM applications. These devices can be physically integrated, at least in part, with the control, inverter, and motor. The present invention provides the necessary power supply voltages from a single motor control.
The zero-sequence voltage or current produced by a PWM inverter can be used to drive a three-phase transformer with the individual phase secondaries of the transformer connected in series to produce a suitable waveform.
The invention provides a method for reverse power conversion in which energy is converted from the low voltage dc side back to the high voltage dc power source.
One advantage of the invention is that the use of zero-sequence currents does not generate any additional torque.
The invention also enables a reduction in the size and reduction in manufacturing cost of the motor drives and accessory power systems.
The invention may be applied to induction machines as well to as permanent-magnet (PM) machines and synchronous machines. As used herein, the term xe2x80x9cmachinesxe2x80x9d shall include both motors and generators.
The invention may be practiced with 2-phase modulation which lowers the switching losses of the main inverter.
Other objects and advantages of the invention, besides those discussed above, will be apparent to those of ordinary skill in the art from the description of the preferred embodiments which follows. In the description reference is made to the accompanying drawings, which form a part hereof, and which illustrate examples of the invention. Such examples, however are not exhaustive of the various embodiments of the invention, and therefore reference is made to the claims which follow the description for determining the scope of the invention.